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Apart from long-known and applied nanostructures like carbon black for tyres or pigments for coatings nanotechnology has created highly sophisticated structures used for nano/molecular electronics,diagnostics,drug delivery, UV-absorbers etc.Often the main question to be solved analytically is the local determination of tiny amounts of chemicals resulting in an ever increasing need for highly sensitive as well as locally resolved techniques.Applications of techniques like mass spectroscopy,transmission el... 相似文献
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Four new fulgimides possessing a fluorescent coumarin unit were synthesized from the corresponding fulgides, and their photochromic as well as fluorescence properties were investigated. The open-ring forms of coumarin fulgimides were found to exhibit fluorescence in the visible region. Upon exposure to UV light, the fulgimides were transformed into the nonfluorescent closed-ring forms, which can be reverted to the initial fluorescent open-ring forms on exposure to visible light. The efficiency of quenching of fluorescence was as high as 95% at the photostationary state of UV irradiation. 相似文献
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The classical limit of the nuclear shell model is shown to be a many-dimensional hamiltonian system in which the coordinates and momenta are the coherent-state parameters of the original quantum system. Several methods for semiclassical quantization of this system are discussed, including surfaces of section and the Birkhoff-Gustavson transformation to action-angle variables. Application to a schematic three-level shell model indicates some of the new problems involved in requantizing multi-dimensional systems which are not present in one-dimensional examples. These include difficulties in finding periodic orbits and the onset of stochasticity. 相似文献
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We have performed axially symmetric Skyrme force time-dependent Hartree-Fock calculations for the 136Xe + 209Bi system at E(lab) = 940 MeV and 1130 MeV. The evolution of the nuclear geometry is studied in detail. The calculated final fragment kinetic energies, scattering angles, and charges are in good agreement with experiment, but the fragment charge dispersion is greatly underestimated. Studies of head-on collisions for 900 MeV ? E(lab) ? 2000 MeV show no evidence for fusion and indicate a dramatic transparency for E(lab) ? 1500 MeV. 相似文献
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用具有大能隙的本征半导体(SrTiO3及SnO2)粉末作本体,分别掺杂1%(原子百分数)的Eu2O3;所得物质表现出Eu3+离子的线发射光谱特性,但相对发光强度及光谱形状有相当大的变化。X射线衍射结构分析显示Eu3+在SrTiO3晶格里是处在间隙位置,而它在SnO2晶格里则形成新物相Eu2Sn2O7。 相似文献
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Two-pion inclusive spectra from relativistic heavy-ion collisions are related to single-particle inclusive measurements in a Lorentz-invariant formulation of the Hanbury-Brown-Twiss effect. A thermal pion source with a gaussian space-time distribution is assumed. The angular anisotropy and moments of the correlation function are computed to facilitate the determination of pion source parameters from the ratios of the two-pion to single-pion inclusive data. 相似文献
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Y. Alhassid G. Maddison K. Langanke K. Chow S. E. Koonin 《Zeitschrift für Physik A Hadrons and Nuclei》1985,321(4):677-685
We have performed Monte Carlo calculations to estimate the exact energies of model problems for4He and theL=0,1, and 2 states of6Li. Using a Feynman path-integral expression for the imaginary-time evolution operator, we recast the ground state energy as a sum over histories, which are then sampled stochastically. Use of a trial wave function dramatically improves the efficiency of the Monte Carlo method. For a state-independent Malfliet-Tjon potential, together with the Coulomb interaction, we find a ground state energy of ?28.00+0.20 MeV for4He, and a degeneracy of theL=0,1, and 2 states in6Li at about ?59.65+-0.50 MeV. Density distributions for these nuclei are also calculated. 相似文献
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FLUORESCENCE ENERGY TRANSFER BETWEEN DIMETHYLDIAZAPEROPYRENIUM DICATION AND ETHIDIUM INTERCALATED IN POLY d(A-T) 总被引:2,自引:0,他引:2
JEAN-LOUIS MERGNY ANNY SLAMA-SCHWOK THÉRÈSE MONTENAY-GARESTIER MICHEL ROUGÉE CLAUDE HÉLÈNE 《Photochemistry and photobiology》1991,53(4):555-558
Dimethyldiazaperopyrenium is one of the largest known DNA intercalators. Fluorescence energy transfer occurred between dimethyldiazaperopyrenium (donor) and ethidium (acceptor) when these dyes were bound to a double-stranded polynucleotide such as poly d(A-T). The addition of increasing amounts of ethidium bromide led to a marked shortening of the fluorescence lifetime of the donor, whereas the excited state of the acceptor was progressively populated via energy transfer from the donor. Critical Förster distance between these two chromophores was calculated to be 3.8 nm. The observed transfer efficiency was lower than that calculated on the basis of this critical distance and a statistical distribution of bound drugs. These results are discussed taking into account the conformational change induced by intercalation of dimethyldiazaperopyrenium in the double-stranded polynucleotide. 相似文献